FIG. 7 shows a reflector supporting mechanism which has been used and FIG. 8 is an extended view of a supporting mechanism part thereof.
In these diagrams, reference numeral 1 denotes a reflector, 2 is a cylindrical sleeve, 3 is a cylindrical socket, 4 is a lateral support lever for supporting in a lateral direction, 5 is a universal joint (fulcrum), 6 is a mirror cell for supporting the reflector, and 7 is an axial support lever for supporting in an axial direction.
Operation is described below. When a telescope is operated, a position of a reflector 1 is changed from a position facing the zenith to a position facing horizontal direction. The reflector 1 can be held by a supporting force of a supporting mechanism which acts in an axial direction and a lateral direction. Since an aluminum deposited on the reflection surface of the reflector 1 deteriorates along with lapse of time, the reflector 1 is removed from the telescope and the reflection surface is re-deposited several times a year. Therefore, a supporting mechanism which can be easily removed from the reflector is required and the supporting mechanism therefor is constructed so that a socket of the supporting mechanism is inserted into a sleeve 2 of the reflector.
Another conventional example is a supporting mechanism for a reflector which actively maintains an accuracy of a mirror surface by carrying out compensation in accordance with a result of measurement of deformation of a large-sized telescope.
FIGS. 9 and 10 show an actuator system related to a conventional large-sized infrared telescope (JNLT) disclosed in Astronomy Monthly "Active Optics of JNLT", December 1989 (Ie and Yamashita), wherein 1 is a reflector, 10 is a sub reflector, 11 is a supporting force detector, 12 is an actuator, and 13 is a mirror surface inspection unit. FIG. 10 shows an extended sectional view of the actuator 10 wherein 17 is a balance weight.
The following describes operation thereof. The large-sized reflector 1 (diameter: approximately 8 m) is supported by a number of actuators 12 (approximately 300 actuators) and the shape of the mirror surface is maintained in a high accuracy (approximately 0.1 .mu.m) by carrying out supporting force analysis/calculation of mirror surface errors in 14 according to an output from the supporting force detectors 11 built in respective actuators 12 and image analysis/calculation of mirror surface errors in 15 according to the output from the mirror surface detection unit and the supporting force is compensated in 16 and therefore high precision actuators are required.
Though an ideal supporting mechanism of the reflector is such that the axis of the socket 3 is positioned in the same direction as the axial direction of the reflector 1, the conventional supporting mechanism includes a problem that the axis deviates when the position of the reflector 1 is changed.
This axial deviation is described below referring to FIGS. 11A to 11F and FIG. 12.
FIG. 11A shows the reflector 1 faced to the zenith, FIG. 11D shows the reflector 1 faced to the horizontal direction, FIGS. 11B and 11C respectively show the position of the reflector 1 whose angle of elevation is changed from the zenith to the horizontal direction, an FIGS. 11E and 11F respectively show the position of the reflector 1 whose angle of elevation is returned from the horizontal direction to the zenith. 20 denotes an axis of the socket 3 and 21 denotes the axial direction of the reflector 1 (axial direction of the mirror).
As shown in the drawing, the axis 20 of the socket 3 is deviated from the axial direction 21 of the reflector 1 due to a change of the angle of elevation of the reflector 1. This deviation is shown in FIG. 12. FIG. 12, (a) to (f) respectively show a status corresponding to the status shown in FIGS. 11A to 11F. Specifically, the amount of deviation increases along with the change of the angle of elevation of the reflector I from the position where the reflector 1 is faced to the zenith as shown in (a) to the position where the reflector 1 is kept in the horizontal direction and the amount of deviation from the status of the reflector faced in the horizontal direction shown in (d) to the status of the reflector faced to the zenith shown in (a) differs from that from the status shown in (a) to the status shown in (d).
The conventional supporting mechanism comprises a sleeve 2 provided with a cylindrical hole and a socket 3 provided with a flange. Though it is ideal that the sleeve 2 and the socket 3 contact each other at the flange and the cylindrical side surface, there is provided a clearance between the sleeve 2 and the socket 3 for remounting the reflector 1 and the axial deviation of the reflector 1 is caused by the change of the relative positions of the sleeve 2 and the socket 3 resulting from the change of attitude of the reflector 1 since there are errors in the dimensions and shapes of parts of the sleeve 2 and the socket 3 which come in contact. The amount of deviation when the angle of elevation increases differs from that when the angle decreases, due to a friction between the sleeve 2 and the flange of the socket 3. Accordingly, there has been a problem that the supporting point positions are deviated or a difference of the supporting force is caused. It has been very difficult to insert the cylindrical socket into the cylindrical sleeve and therefore there has been an inconvenience in remounting the supporting mechanism.